The present invention relates to an intake manifold for internal combustion vee-engines, and to a method of manufacturing the intake manifold.
In an arrangement of the conventional intake manifold for internal combustion vee-engines, two branch passage portions branch from one end of an intake pipe portion or an inlet passage portion connected to a substantially central section of the intake manifold, as disclosed, for example, in Japanese Patent Application Laid-Open no. 57-119155. The two branch passage portions extend in a curved fashion in their respective directions opposite to each other, and communicate respectively with intake passages provided respectively in left and right cylinder banks.
However, the above-described conventional arrangement has various problems. That is, because both branch passage portions are formed in a curved fashion, the intake manifold becomes complicated in structure. Not only does this result in an increase in the cost, but also makes it impossible to cast the intake manifold by means of metal dies. If the intake manifold is cast by means of molds other than the metal dies, it is necessary to employ cores, resulting in an increase in the cost. Variation is large in the contour of the cast products, in particular, in the contour of the passages for the intake mixture, so that the engine performance is rather scattered. Considerably extensive machining is required for the cast intake manifold. Moreover, if a water channel for cooling water after having cooled the engine is desired to be formed in parallel with the branch passage portions to preheat intake mixture flowing therethrough, the intake manifold is further complicated in structure, making it difficult to cast the intake manifold.